A wide variety of procedures and different types of equipment are available for use in recapping or retreading pneumatic tires. One of the first steps in retreading a worn tire is to remove existing tread material from the tire carcass by buffing. Various procedures are available to apply one or more layers of uncured rubber or retreading material with appropriate bonding agents to the buffed tire carcass. The uncured rubber may also be stitched to the buffed carcass as required. For purposes of this patent application, the term "casing" is used to refer to a buffed tire carcass which has been built up with one or more layers of uncured rubber and other material as required by the retreading equipment and procedures being used to rebuild the worn tire.
In the past, heavy duty mechanical and/or hydraulic closing devices have often been used to install molds which form a new tread in retreading material on a prepared tire carcass or casing. Tire distortion sometimes occurs as the tread molds are closed on the casing. This problem is particularly common if the casing is slightly larger in diameter than desired. In such cases, the prepared tire carcass will often buckle and can thus no longer be used. Damage to a casing during mold installation represents a substantial loss of time and material spent preparing the tire carcass for mold installation.
One method of recapping or retreading tires is illustrated in U.S. Pat. No. 4,767,480, issued Aug. 30, 1988 to Leon C. Goldstein. This patent describes apparatus and methods for retreading which uses a cold process. In this process, a flexible tread mold is stretched over the tire carcass. Subsequently, an envelope is placed over the mold and prepared tire carcass and the entire unit or assembly is placed in a chamber where curing of the rubber is accomplished by inflation of the tire carcass, evacuation of the envelope and pressurization of the chamber and the application of heat.
U.S. Pat. No. 4,588,460, issued May 13, 1986 to Arthur W. McGee, et al. illustrates another method and apparatus for retreading a tire that includes a relatively flexible mold which is formed by a plurality of mold segments. The ends of adjacent mold segments include guides so that the mold, when closed, will form a circle about the casing which will be retreaded. In this process, an elastic band encircles the mold segments for the purpose of holding the mold in position on the tire during handling such as when an envelope is placed over the tire which is ultimately pressurized to force the mold segments into the uncured retread material encircling the tire.
Pneumatic tires may also be recapped or retreaded by installing a continuous replacement tread on a prepared tire carcass. Both uncured and cured or vulcanized rubber compounds have previously been used to provide the continuous replacement tread. Examples of equipment and procedures used to install continuous replacement treads on a tire casing are shown in U.S. Pat. No. 3,976,532 to C. K. Barefoot; U.S. Pat. No. 4,088,521 to P. H. Neal; U.S. Pat. No. 4,036,677 to Carlo Marangouri; and U.S. Pat. No. 4,957,574 to A. R. Clayton, et al.
Most retreading procedures also require the use of a flexible envelope to seal around the tire casing, retread material and tread mold (if used). The complete assembly, including the tire casing, retread material, tread mold (if used) and envelope, are placed in a high pressure, high temperature chamber in preparation for curing the components which comprise the completed tire assembly. The high pressure, high temperature chamber is frequently referred to as an autoclave. Examples of a tire retreading envelope and high pressure, high temperature curing chamber are shown in U.S. Pat. No. 4,309,234 to P. L. Witherspoon. As noted above, U.S. Pat. No. 4,767,480 also contains information on the use of envelopes to assist with curing retreaded tires.
The above listed patents are incorporated by reference for all purposes within this application.